The present invention relates to an apparatus for transmitting motion to a load, and, in particular, relates to an apparatus for providing a support to the load after the load has been translated to an extended position.
One prior device for holding the load in the extended position was an external latching means being different from the device for providing the translation to the extended position.
In addition, prior motion-transmitting devices cannot successfully withstand resistance to corotation of the driving and driven elements beyond a certain degree. If the resistance is applied suddenly, as when the output element or member strikes a stop or otherwise freezes, the backlash damages the parts of the device and can even break an input element such as a shaft. Even if the resistance to corotation is gradually increased, a stalling point is eventually reached at which the resistance overcomes the driving force and the driving element is brought to rest. In those application where the driving element is the shaft of or connected to an electric motor, even a gradual overcoming of the driving force can burn out the motor or inflict other damage.
Where prior motion-transmitting devices are used to convert rotary motion into translatory motion, still other problems are met. When, for example, the end of a translatory movement is reached, as by striking a stop, the output translatory element is often found to bind or otherwise become so impacted on the stop that it is not possible to retract the element back toward its starting point. As an instance, a threaded shaft may be rotated as by a motor to move a nut on the threaded shaft in a translatory or axial direction thereof. When the nut strikes a stop, particularly if the member rams against the stop in a sudden jarring impact, the nut may become skewed on the shaft or otherwise bound on the shaft or the stop. When it is subsequently attempted to reverse the motor and rotate the threaded shaft in the opposite direction and thereby retract the nut it is often found that the motor lacks sufficient power to withdraw the member.
To avoid some of the foregoing problems, it has been suggested to allow the translatory element to rotate freely upon striking a stop or "freewheel". For instance, in the above example, the nut can rotate freely or freewheel on the threaded shaft after striking a stop in the manner illustrated in U.S. Pat. No. 2,446,393 to Russell. However, in such construction there is freewheeling only when axial movement of the nut along the threaded shaft is absolutely blocked. That is, there is no control on the minimum amount of resistance to corotation of the driving and driven elements which is necessary to initiate freewheeling.
These drawbacks have motivated a search for a device that cannot only extend a load but support the load when extended.